Energy saving system for a display apparatus based on image change detection

Abstract: A display apparatus includes a power supply to be stopped in a low-power consumption mode, a unit for displaying an image based on image data input from a computer or television, a unit for outputting a first transfer signal for stopping the power supply based on a first control signal for controlling transfer to the low-power consumption mode, which is input from the computer or television, a unit for outputting a second transfer signal for stopping the power supply based on the input image data, and a power supply control means for stopping the power supply based on the first and second transfer signals.

Description: The present invention relates to a display apparatus for a computer terminal monitor, a camera view finder, a television receiver, a projector, etc. Particularly, the present invention relates to a display apparatus capable of controlling, on the basis of different signals, power supplied from a power supply. Since there are demands for energy saving of office automation apparatus such as computers, and terminal monitors thereof, for example, regulations on energy saving are established by some institutions. In accordance with the regulations on an energy-saving monitor, the energy-saving monitor must be set so that the power consumption of the monitor is decreased to 30 W or less a predetermined time after the operator of a computer stops using a keyboard. Examples of measures for satisfying these regulations are as follows: 1. A computer device, for supplying image signals, adapted to superimpose, on a monitor synchronous signal, information that a predetermined time has passed after the operator has stopped using a keyboard. The monitor decodes the information, and controls the power consumption of the monitor to force it to decrease on the basis of the information. 2. A computer device, for supplying image signals, adapted to change image data into predetermined data and output the data to the monitor side after the passage of a predetermined time after the operator has stopped using the keyboard. The monitor discriminates the image data, and, when predetermined image data is continuously sent for a predetermined time, controls the power consumption of the monitor itself to force it to decrease. 3. A monitor that makes a decision as to whether or not image data sent from a computer device has changed, and, if the image data has not changed for a predetermined time, controls the power consumption of the monitor itself to force it to decrease. However, in the case of measures 1 and 2 above, when the monitor itself has a need to transfer to the low-power consumption mode, it is impossible to transfer it to the low-power consumption mode unless a demand for the low-power consumption mode is sent from e.g. an external computer or television receiver. It is thus impossible to realise transfer to the low-power consumption mode at as short intervals as possible for reducing power consumption and e.g. increasing the life of a back light in the monitor. Although, in case of measures 1 and 2, a new function must be added to a computer or television receiver, even if the low-power consumption mode function is provided on the monitor side in an old type computer or television receiver, the system cannot comply with the function. In the case of measure 3 it is a problem that when a cursor flicker or a time is to be displayed, even if the user does not use the keyboard, image data is always changed, thereby making it impossible to transfer to the low-power consumption mode. An example of measure 3 is given in EP-A-0525786. This discloses a display apparatus of the kind having a display device for displaying an image on the basis of received input image data, and including a control circuit for controlling the level of power consumption, and which is operable to transfer operation of the display apparatus from a first mode of predetermined power consumption level to a second mode of lower power consumption level, wherein said control circuit includes detection means for detecting changes between currently input image data and previously input image data; transfer means, co-operable with said detection means, for transferring operation of the apparatus from said first mode to said second mode in the event that said detection means detects no change in the compared input image data; and receiving means for receiving an externally applied demand signal (a) to instruct a change of the power consumption mode , which demand signal is different from image data. As disclosed therein, the time interval for detecting any change in the compared input image data is adjustable in response to this externally applied demand signal. A similar example is given in EP-A-0494610 in which input image data to be written into a video RAM is compared with that image data already stored. When there is no change in the compared image data, no further image data is transferred from the video RAM to the display panel and no rewriting is conducted. The above discussed problems have now been addressed and the present invention is presented as a solution. In accordance with the present invention, a display apparatus of the kind just described is characterised in that said transfer means also is co-operable with said receiving means for independently transferring operation of the apparatus from said first mode to said second mode in response to the receipt of said demand signal not withstanding said transfer means also is co-operable with said receiving means for independently transferring operation of the apparatus from said first mode to said second mode in response to the receipt of said demand signal, notwithstanding the detection by said detection means of changes between the current input image data as previously input image data. It is convenient to provide apparatus as aforesaid having provision for at least one power supply and wherein said transfer means is responsive to first and second transfer signals output respectively by said detection means and by said receiving means for switching off or adjusting said at least one power supply if either no change in input image data is detected as aforesaid or said demand signal is received. In the present invention, the components below can appropriately be selected and employed as optional means. It is preferable to provide means for outputting a first start signal for starting the power supply on the basis of the first control signal, and means for outputting a second start signal for starting the at least one power supply on the basis of the input image data. In this case, the transfer means switches on the at least one power supply on the basis of the first and second start signals. The transfer means may include timer means for adjusting the time taken from the receipt of the first or second transfer signal to the transfer of operation from the first mode to the second mode. The control circuit preferably also has switching means for outputting a signal for releasing the low-power consumption mode. In this case, the transfer means switches on the power supply on the basis of this signal. When there are a plurality of power supplies for driving the display means, which are respectively switched off by the first and second transfer signals, if the first and second transfer signals compete with each other, the transfer means performs logical operation of the signals based on predetermined logic, and selectively stops the plurality of power supplies on the basis of the results of the operation. Alternatively, the transfer means selects a signal with higher priority based on predetermined logic and selectively stops the plurality of power supplies on the basis of the selected signal. In this case, it is preferred to provide means for changing the predetermined logic. The image display means has, for example, a liquid crystal panel and a back light for illuminating the panel. In this case, the power supply for driving the liquid crystal panel and the power supply for the back light which is actuated separately therefrom are switched off in the low-power consumption mode. In the above-described construction, when the first transfer signal is output, the transfer means switches off the power supply on the basis of the first transfer signal to transfer to the low-power consumption mode. When the second transfer signal is output on the basis of the input image signal, similarly, the power supply is stopped to transfer to the low-power consumption mode. Namely, transfer to the low-power consumption mode is performed by decision by the display apparatus itself based on the input image data. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram illustrating a display apparatus in accordance with an embodiment of the present invention; Fig. 2 is a block diagram illustrating a monitor system (display apparatus) in accordance with another embodiment of the present invention; and Fig. 3 is a block diagram illustrating a control section for controlling low-power consumption and the peripheral portion thereof of the monitor system shown in Fig. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a block diagram illustrating a control system of a display apparatus in accordance with an embodiment of the present invention. In Fig. 1, reference numeral 201 denotes an input unit comprising a keyboard, a mouse, etc. Reference numeral 202 denotes an image memory for storing an image signal output from an image signal generator (e.g., an image scanner, a television tuner or the like), which is not shown in the drawing. Reference numeral 203 denotes a detector for detecting a change in the signal stored in the image memory. Reference numeral 204 denotes a control circuit for transmitting a signal to one of signal generators 205 and 206 when receiving a signal from one of the input unit 201 and the detector 203. Reference numerals 205 and 206 each denote the signal generator for generating a signal for switching display modes. Reference numeral 207 denotes a display controller for selecting one of a plurality of display modes and executing the selected mode. Reference numeral 208 denotes a display for displaying an image in accordance with the selected display mode. The display 208 has a power supply, display means such as a liquid crystal panel, etc. The display controller 207 receives first or second transfer signals as instructions to transfer to a second mode (low-power consumption mode) from a first mode from the signal generators 205 and 206. The first transfer signal is generated in response to the first control signal output from the input unit 201, and the second transfer signal is generated in response to the detection signal from the detector 203. The display controller 207 also switches the display modes when receiving the first and second transfer signals. The display modes may be modes for different power consumptions, and power consumption is appropriately determined by limitations in an area where the apparatus is used, the type of information to be displayed, the size of the display, etc. At least in the low-power consumption mode, one is selected from a method of decreasing the quantity of light of the back light, a method of turning off the back light, a method of decreasing the driving voltage, and a method of increasing the refresh scanning period, and is executed. The low-power consumption mode is returned to the normal mode in response to the signal output from the input unit 201 or the detector 203. If required, mode changes are provided with priorities so as to add the function to return to the normal display mode when an image on the memory 202 is rewritten even if the signal for transferring to the low-power consumption mode is generated from the input unit 201. Fig. 2 is a block diagram illustrating a system comprising a display apparatus in accordance with another preferred embodiment of the present invention. In Fig. 2, reference numeral 20 denotes a monitor; reference numeral 1, a computer or television for supplying image data to the monitor; reference numeral 2, a synchronous signal generating section for superimposing, on a synchronous signal for the monitor 20, a signal for requesting the monitor 20 to transfer to the low-power consumption mode of the computer or television 1; reference numeral 3, a timer for determining a time required before executing the low-power consumption mode after the user stops input from a keyboard; reference numeral 4, the keyboard as an input device for the user; reference numeral 5, a decoding section for detecting a low-power consumption mode demand on the basis of the synchronous signal sent from the computer or television 1; reference numeral 7, an image data setting section for setting image data which indicates a demand for the low-power consumption mode; reference numeral 6, a detection section for detecting a low-power consumption mode demand by comparing image data sent from the computer or television 1 with optional image data input from an image data setting section 7; reference numeral 8, a rewrite detecting section for detecting a change in the amount of image data sent from the computer or television 1; reference numeral 9, a rewrite deciding section for deciding as to whether the image data is rewritten or merely changed due to noise; reference numeral 10, a condition setting section for setting decision criteria for the rewrite deciding section 9; reference numeral 11, a timer group for receiving three low-power consumption mode transfer signals sent from the decoding section 5, the detection section 6 and the rewrite deciding section 9 and setting the time required for transferring to each of the modes; reference numeral 12, a timer setting section for setting the times of the timer group 11; reference numeral 13, a control section for receiving each of the low-power consumption transfer signals from the timer group 11 and sending each of the low-power consumption mode transfer signals to a panel controller 15; reference numeral 14, a release section for releasing the low-power consumption mode; reference numeral 15, the panel controller for receiving each of the low-power consumption mode transfer signals from the control section 13 and controlling each of the power supplies of the monitor 20; reference numeral 16, a power supply for driving the panel; reference numeral 17, a power supply for a back light; reference numeral 18, a power supply for the panel controller 15; reference numeral 19, a panel unit (the panel, panel driving circuit, back light); and reference numeral 21, a switching section required for switching the control methods of the control section 13. Fig. 3 is a block diagram illustrating the control section 13, the timer setting section 12, the timer group 11, etc. As illustrated in Fig. 3, the timer setting section 12 and the timer group 11 have three timer setting sections and three timers connected thereto, respectively, in correspondence with the three low-power consumption mode transfer signals. The procedure for transferring to the low-power consumption mode is described in detail below. The monitor 20 uses control signals (transfer signals) for transferring to first to third low-power consumption modes from the control section 13, and transmits each of the low-power consumption mode demands to the panel controller 15 on the basis of the control signals and information stored in the control section 13. The procedure for generating the control signal (transfer signal) for the first low-power consumption mode is first described below. The timer 3 of the computer or television 1 measures the elapsed time since the user has stopped using the keyboard 4. When a predetermined time has elapsed, the synchronous signal generating section 2 superimposes a low-power consumption mode demand signal on the synchronous signal. The superimposing method may be a method of changing the pulse width of the synchronous signal to denote a chosen low-power consumption mode, or a method of changing the level of the synchronous signal. When the monitor 20 receives the synchronous signal, the low-consumption mode decoding section 5 detects and low-power consumption mode demand from the pulse width or the level. The detection information is sent to the timer group 11, and then to the control section 13 after the elapse of the time set by the timer setting section 12. The procedure for generating the control signal for the second low-power consumption mode is described below. The timer 3 of the computer or television 1 measures the elapsed time since the user has stopped using the keyboard 4, and after a predetermined time has elapsed, the computer or television transmitter image data predetermined by the monitor 20. In the monitor 20, predetermined image data is set in the image data setting section 7. The image data detecting section 6 of the monitor 20 compares the image data sent from the computer or television 1 with the image data previously set in the image data setting section 7. When both image data are the same, the monitor recognises a low-power consumption mode demand, and transmits recognition information to the timer group 11. The timer group 11 transmits the information to the control section 13 after the elapse of the time set by the timer setting section 12. The first and second low-power consumption modes are released when either the user uses the keyboard 4, or image data from the computer or television, connected to the monitor 20, is changed by access thereto from the outside through a network. When a change in the image data is detected, the synchronous signal and the image data are changed to the normal mode in the computer or television 1. At the same time, the release signal is generated in each of the low-power consumption mode decoding section 5, and the image data detecting section 6, and transmitted to the control section 13 through the timer group 11. When the control section 13 receives the release signals, the release information is transmitted to the panel controller 15 to turn on each of the power supplies, which are previously turned off. The procedure for generating the control signal for the third low-power consumption mode is described below. The rewrite detecting section 8 of the monitor 20 detects a change of the image data while monitoring the image data output from the computer or television 1 regardless of information output therefrom after the user stops using the keyboard 4. Namely, the level of the image data for the previous frame which is stored in a frame memory for one frame, is compared with the level of the present image data at the same position, and a difference between the two levels is detected. Alternatively, a characteristic of the image, e.g., a rate of vertical or horizontal change of the image data, or the run length of the image data, may be compared with the characteristic of the previous frame data, and a difference may be detected. When the above difference is detected, data indicating the difference is transmitted to the rewrite deciding section 9. The rewrite deciding section 9 decides whether the transmitted image data difference is due to external noise or to a rewrite by the user. Although conditions for returning to the low-power consumption mode are established only when the image data difference is zero, when the image data transmitted from the computer or television 1 has analog values, and when noise is produced in the transmission system, a slight image data change is detected even if the image data is not changed by the user, thereby forming no control signal for transferring to the low-power consumption mode. In consideration of the noise, therefore, when the image data difference is smaller than the value set by the condition setting section 10, it is decided that the image data is not changed, and information of the low-power consumption mode is sent to the timer group 11. The timer group 11 transmits the information to the control section 13 after the elapse of the time set by the timer setting section 12. The control section 13 observes the three low-power consumption mode signals on demand, and transmits the control signal for low-power consumption optimum for the panel unit 19 to the panel controller 15. Namely, the control section 13 has priorities of the three low-power consumption mode control signals, and simple combinational logic means, as illustrated in Fig. 3, so that the control signal for low-power consumption to be transmitted to the panel controller 15 can be changed. For example, with the priorities, when the control section 13 receives the first low-power consumption mode control signal after a signal for controlling the panel driving power supply 16 to turn it off by the third low-power consumption mode control signal is transmitted to the panel controller 15 or at the time of transmission of the signal, the low-power consumption control signal of the panel specified by the first low-power consumption mode control signal is transmitted. This accords priority to a demand to execute the low-power consumption mode, which is given from the computer or television 1, and is thus effective for satisfying the standard specifications of the low-power consumption mode determined by the computer or television 1. The combinational logic means permits control in accordance with the levels of the specifications for low-power consumption of the computer or television 1 connected to the monitor 20. For example, when the monitor 20 is connected to the computer or television 1 which does not satisfy the specifications for superimposing the low-power consumption mode on the synchronous signal for generating the first low-power consumption mode control signal, AND of the first low-power consumption mode control signal and "0" prevents the control section 13 from receiving an incorrect control signal. For example, when it is desired to make all of the first, second and third low-power consumption modes effective, this can be realized by ORing all control signals. The control section 13 transmits the required low-power consumption control signal to the panel controller 15 in accordance with the priorities and combinational logic. The priorities and combinational logic are controlled by a microcomputer and can be changed by the user from the outside through the switching section 21. The control section 13 also has the function to release the low-power consumption mode by the monitor 20 itself. This is required when the normal mode is transferred to the low-power consumption mode by the third low-power consumption control signal with the back light 17 turned off, and when the user desires to recognize display contents even if the image data is not changed. The user can force the low-power consumption mode to be released by the release section 14 having a device such as a switch or the like provided on the monitor 20 to turn the back light on. When the rewrite deciding section 9 decides that the image data is rewritten by a cause of some kind, the decision signal is of course transmitted to the control section 13, and to the panel controller 15 through the control line c shown in Fig. 2 for controlling the back light 17 to turn it on. The power supply 18 for the panel controller 15 required for release always remains turned off regardless of control by the control section 13. The contents of the low-power consumption control signal include turning-off of the panel driving power supply, turning-off of the back light power supply, and turning-off of both power supplies. The low-power consumption control signal may be transmitted through the dedicated control signal line c , or superimposed on a portion of an image data bus c for transmitting the image data to the panel controller 15. Although, in Fig. 2, the image data is transmitted to the panel controller 15 from the rewrite detecting section 8, this is because a monitor having memory such as a ferroelectric liquid crystal panel may receive only the image data in the rewritten portion. A monitor without memory may receive image data directly from the computer or television 1. Although the panel controller 15 can receive the control signal on demand, it has a control section for controlling the time of turning off the panel driving power supply 16. This is effective for a device such as a liquid crystal panel which produces deterioration in the panel when a DC voltage is applied thereto. When the panel controller 15 receives the control signal for turning off the panel driving power supply, the power supply is not immediately turned off, but turned off at the time no write voltage is present in the panel after one line is completely written. This prevents application of the DC voltage to the panel. As described above, the transfer to a low-power consumption mode and the release from the low-power consumption mode are based on decisions taken by the display apparatus itself. A computer or television which does not satisfy low-power consumption specifications thus can comply with the low-power consumption specifications on the display apparatus side. On the other hand, since it is possible to transfer to the low-power consumption mode and release the low-power consumption mode by the control signal for controlling the transfer to the low-power consumption mode, which is output from the outside, a computer which satisfies the low-power consumption specifications has the effects in accordance with the specifications. It is also possible to increase the life of the apparatus by turning off the back light at short intervals according to the circumstances on the display apparatus side.

Claims: A display apparatus having a display device (19) for displaying an image on the basis of received input image data, and including a control circuit (8-13,15) for controlling the level of power consumption, and which is operable to transfer operation of the display apparatus from a first mode of predetermined power consumption level to a second mode of lower power consumption level, wherein said control circuit includes: detection means (8,9) for detecting changes between currently input image data (b) and previously input image data; transfer means (11-13,15), co-operable with said detection means, for transferring operation of the apparatus from said first mode to said second mode in the event that said detection means detects no change in the compared input image data; and receiving means (5) for receiving an externally applied demand signal (a) to instruct a change of the power consumption mode, which demand signal is different from image data; which apparatus is characterised in that : said transfer means (13,15) also is co-operable with said receiving means (5) for independently transferring operation of the apparatus from said first mode to said second mode in response to the receipt of said demand signal, notwithstanding the detection by said detection means (8,9) of changes between the current input image data as previously input image data. A display apparatus according to claim 1 having provision for at least one power supply (16,17) and wherein said transfer means (11-13,15) is responsive to first and second transfer signals output respectively by said detection means (8,9) and by said receiving means (5) for switching off or adjusting said at least one power supply (16,17) if either no change in input image data is detected as aforesaid or said demand signal is received. A display apparatus according to claim 2 wherein said transfer means (11-13,15) is responsive to first and second start signals output respectively by said detection means (8,9) and by said receiving means (5), for switching on or adjusting said at least one power supply (16,17) for operation in said first mode. A display apparatus according to claim 2 wherein said transfer means (11-13,15) includes timer means (11,12) for adjusting and for determining a time from receipt of said first or second transfer signal to the transfer from said first mode to said second mode. A display apparatus according to claim 2 further comprising switch means (14) for outputting a release signal for releasing the apparatus from said second mode, and wherein said transfer means (11-13,15) is co-operable with said switch means (14) and is responsive to said release signal to transfer operation in said second mode to operation in said first mode. A display apparatus according to claim 2 having provision for a plurality of power supplies (16,17) wherein said transfer means (11-13,15) includes a logic circuit (13) to perform a logical operation on said first and second transfer signals for selectively switching off said power supplies (16,17) on the basis of the result of said logical operation. A display apparatus according to claim 2 having provision for a plurality of power supplies (16,17) wherein said transfer means (11-13,15) includes a logic circuit (13) to perform a logical operation on said first and second transfer signals such that in the event of said first and second transfer signals competing with each other, said logic circuit shall select that signal accorded higher priority and said transfer means shall selectively switch off said power supplies on the basis of the selected signal. A display apparatus according to either of claims 6 or 7 wherein said logic circuit (13) includes means for changing said logical operation. A display apparatus according to any preceding claim 2 to 8 wherein said receiving means (5) is responsive to said demand signal (a) superimposed on an image data synchronisation signal. A display apparatus according to claim 2 wherein said control circuit (8-13,15) includes comparison means (6,7) for comparing said received input image data with predetermined image data and for outputting a third transfer signal when said received image data and said predetermined image data are the same; and said transfer means (13,15) is co-operable with said comparison means for transferring operation of the apparatus from said first mode to said second mode in response to said third transfer signal. A display apparatus according to any of claims 2 to 10 including: a liquid crystal display panel as said display device (19); a back light for illuminating said display panel; and, as said at least one power supply, first and second power supplies (16,17) for driving said display panel and for operating said back light, respectively. A display apparatus according to any preceding claim wherein said detection means detects said changes by one of comparing the levels of the compared input image data, or compares extracted characteristics of images represented by the compared input image data, or compares run lengths of the compared input image data. A display system comprising: a display apparatus (20) according to any preceding claim; and a computer or a television receiver (1) co-operable with said display apparatus for supplying said input image data (b) and said demand signal (a).

Inventors: MIYAMOTO KATSUHIRO, MIYAMOTO, KATSUHIRO, MIYAMOTO, KATSUHIRO, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: G09G3
IPC codes: G09G5, G09F9, G09G3, G06F1, H02J1, G02F1, H04N5